1. Field of the Invention
The present invention concerns the radial displacements of at least two mechanical parts adjacent to one another, in particular for steerable drilling applications. It concerns in particular drilling which requires accurate trajectory control, in particular in the fields of the petroleum and gas industry, civil engineering, geothermics and more generally in all fields of trenchless underground operations, or even the accurate steering of mechanical parts, such as rolling mill rollers, in particular.
The invention concerns more particularly, whatever the application envisaged, an annular device providing for controlled essentially radial displacements and/or stresses between at least two mechanical parts with a common axis in one or two directions.
2. Description of the Prior Art
Drilling tool steering devices have been described for example in documents WO 90/07625, U.S. Pat. Nos. 6,581,699 and 2,898,935.
These devices meet certain objectives but they do not always make it possible to achieve the best results in all circumstances.
It is generally proposed to use hydraulic radial or tangential jacks, which equates to a simple, reliable and reversible design. But such jacks generally operate at high pressure and offer short travel in such an environment. Furthermore, they are difficult to instrument in order to obtain accurate position control.
Document U.S. Pat. No. 3,677,354 recommends the use of inflatable cushions for displacement in a plane in two directions in a very restrictive annular environment. These offer a high load and expansion capacity with low operating pressures, but they are fragile, especially at high temperature, and lack rigidity.
Document U.S. Pat. No. 5,875,859 suggests using double eccentric systems, which are capable of generating very great stresses and managing a multitude of positions with great accuracy. But the design of these systems makes them generally irreversible and it is essentially proposed that they be associated with needle bearings. Their drive necessitates complex control systems and it generally necessitates two clutches or two independent motor drives.
Also, wedge systems have been proposed, also capable of generating high stresses, but the implementation of which is extremely delicate in an annular space and which are by nature better suited to a unidirectional mode.
It is universally accepted that the reliability of a system is more often inversely proportionate to its complexity, which is itself also an important cost factor, both for manufacture and for maintenance.
According to the present invention, an alternative reversible or irreversible solution has now been developed, radially compact and controllable with accuracy with respect to both stress and position, and also perfectly suitable for drilling, therefore able to operate in the presence of shocks and vibrations, on the basis of research aimed at responding to the above mentioned expectations—in particular those aroused by the attractive nature of the device described in patent FR 2.898.935.